[Primary strength of conventional and alternative suture techniques of the rotator cuff. A biomechanical study]. / Uber die Primärfestigkeit konventioneller und alternativer Nahttechniken der Rotatorenmanschette. Eine biomechanische Untersuchung.

The aim of this biomechanical study was to evaluate rotator cuff repair strength using different suture anchor techniques compared to conventional repair, taking into consideration the native strength of the supraspinatus tendon. Therefore, a defined defect of the supraspinatus was created in 50 freshly frozen cadaver specimen (group size n = 10; median age at death: 56 years). Five methods were employed for cuff repair: standard transosseous suture, modified transosseous suture with patch augmentation and three suture anchors (Acufex Wedge TAG, Acufex Rod TAG und Mitek GII). The maximum tensile load of the five techniques was: standard transosseous suture, 410 N; modified transosseous suture, 552 N; Wedge TAG, 207 N; Rod TAG, 217 N; Mitek GII, 186 N. The difference between the suture anchor and standard techniques were highly significant (P < 0.001). In this series, the Mitek Gll anchor showed the lowest anchor dislocation rate at 3% (n = 1). The Wedge TAG system had a dislocation rate of 27% (n = 8) and the Rod TAG system 43% (n = 13). Suture anchor techniques revealed about 20%, the standard technique 34% and its modification 60% of the hypothetically calculated native tendon strength. Compared to conventional transosseous suture techniques, the use of the suture anchors tested in this series does not significantly increase the primary fixation strength of rotator cuff repair. The metallic implant with two barbs (Mitek GII) seems to be superior to the polyacetal anchors when inserted into the spongiform bone of the greater tubercle. The considerably weaker repair strength needs to be taken into consideration in postoperative patient rehabilitation, especially after the use of suture anchors.

The bow test for the subacromial impingement syndrome.

Because of the biomechanics of the glenohumeral joint, impairment of rotator cuff function leads to cranial migration of the humeral head, impinging the greater tubercle against the coraco-acromial arch and irritating the subacromial bursa. When bursal irritation has become established, active elevation of the arm against gravity will cause pain within an arc of motion. When a patient with a painful arc is asked to bend forward and let the arm hang, the same arc will become painless. This noninvasive clinical test called the "bow test" is a simple means by which subacromial impingement can be clinically identified as the source of pain in the painful arc of shoulder motion.

[Surgical decompression of the fornix humeri, comparison of 2 procedures: resection of the ligament and Neer's method of anterior acromioplasty]. / Operative Dekompression am Fornix humeri, Vergleich zweier Verfahren: Ligamentresektion und vordere Akromionplastik nach Neer.

The impingement-syndrome is caused by a conflict between the humeral head, the rotator cuff and the coracoacromial arch. Degenerative changes in the rotator cuff appear to be the cause when conservative treatment fails, surgical decompression may be resorted to. The two methods commonly applied are the resection of the coracoacromial ligament and Neer's anterior acromioplasty. In this retrospective study 52 patients were followed up of whom 31 had ligament resection and 21 had acromioplasty. The average follow up time was 10 months. Excellent and good results were achieved by ligament resection in 16 patients (52%) and by acromioplasty in 12 patients (57%). Satisfactory results had 10 (32%) patients after ligament resection and 8 patients (38%) after acromioplasty. In 5 cases (16%) unsatisfactory results were achieved by ligament resection and in 1 case (5%) after acromioplasty. Statistically the results did not differ at the 5% level of error. Both methods retain the length of the acromion which is important as it is the attachment of the deltoid muscle and determines the functional lever arm of this muscle. The superior results of acromioplasty in cases with rotator tears suggest that this procedure could be beneficial as a routine decompression in these cases. Theoretically the acromioplasty creates more space for the reconstructed cuff.

Effects of stem design and material properties on stresses in hip endoprostheses.

With the aid of a three-dimensional finite element stress analysis a parameteric study of the essential aspects of the femoral component of hip endoprostheses was carried out. Various designs were investigated; these included the prosthetic stem length, the existence or non-existence of the prosthetic collar and the elastic modulus of stem and cement. Variations in the stem length have only minor effects on the stress distribution for a stem length greater than 100 mm, but the elastic modulus of the prosthetic stem has a considerable influence on the stresses. A high elastic modulus of the stem increases the stresses in the stem but it decreases stresses in the cement. The cement stresses increase with an increase in the modulus of elasticity of the cement.

[Pre and postoperative computerized tomographic diagnosis in tumors of the shoulder girdle]. / Prä- und postoperative computertomographische Diagnostik bei Tumoren des Schultergürtels.

33 CT-investigations of 23 patients with malignancies of the shoulder girdle were analyzed. In 80% of the surgically treated bone tumours of 17 patients the presence and extend of soft tissue infiltration and of osseous destruction could be delineated. The size of the 6 soft tissue tumours was better demonstrated by CT than by any other radiologic procedure. As CT is the most reliable noninvasive method to visualize the extend of a tumour of the shoulder girdle it is a valuable aid in treatment planning. Diagnostic pitfalls and results of follow-up studies are discussed.

[Stresses on the femur following hip joint replacement]. / Die Beanspruchung des Femur nach Hüftgelenkersatz.

The stresses in femur after joint replacement have been calculated with the finite element method and the results were checked by using strain gauges glued on the surface of the femur and on the prosthetic stem. The influence of stem length and prosthetic collar on the distribution of the stresses have been investigated. The stem length has only a minor effect on the stress distribution if the stem has a texture which allows transfer of tension and shear at the interface endoprosthesis--bone cement. Merely at the tip of the stem changes of the stresses are obvious. The stresses in the bone near the resection plane are distinctly reduced if the prosthesis has a collar. These results have very limited relevance for implants with a smooth stem which does not allow the transfer of tension and shear at the interface endoprosthesis--bone cement.

Finite-element-analysis and experimental investigation in a femur with hip endoprosthesis.

The stress distribution in a human femur with an endoprosthesis was determined. The finite element method (FEM) was used for a three-dimensional model with more than 15000 degrees of freedom. Geometrical and material data had been taken for this model from a left femur with endoprosthesis. On the contralateral bone a strain gauge investigation was performed to validate the calculations. Reasonable agreement was achieved. Various modes of loading were investigated. A perfect bond at the interface between materials of different elastic moduli was assumed. The results are valid for endoprosthesis with such structured stem surfaces as allow transfer of tensile and shear stresses.

Finite-element-analysis and experimental investigation of stresses in a femur.

The state of stress of an intact femur was analysed using a three-dimensional finite element model. One of a pair of femora was used for determination of data for the 3-D model. The other was instrumented with 34 rosette strain gauges for experimental measurements. Good agreement of analytical and experimental data was achieved. For six modes of loading, the deflections and the principal and comparison stresses were determined and compared. The upper one third and the diaphysis of the femur are differently affected in their state of stress, by different modes of loading including simulation of the abductor muscles and the iliotibial tract. For qualitative stress studies of the diaphysis, loading by a single force on the femoral head parallel to the shaft axis may be adequate.

[The stresses in femur (author's transl)]. / Die Beanspruchung des Femur. II. Einfluss des Tractus iliotibialis.

The influence of pull in the iliotibial tract on the stresses in the human femur was investigated using the finite element method. Stresses and strains were computed for a model, assuming different forces in the iliotibial tract. The results were experimentally confirmed using strain gauges. The pull in the iliotibial tract mainly reduces the high tensile strains at the lateral side.

[The stresses in femur. I. Intact femur without consideration of the iliotibial tract (author's transl)]. / Die Beanspruchung des Femur I. Intaktes Femur ohne Berücksichtigung des Tractus iliotibialis.

Stresses in femur under different load conditions were computed with the finite element method. The computer model was composed of 1950 spatial elements. The calculated results were confirmed using 34 strain gauge rosettes, attached on the femur surface. The load conditions were chosen as at the stance phase of walking and as standing on two legs. Additionally, the effect of joint forces under different directions were investigated. It is the main conclusion of this work that the computed quantitative results are only relevant when the geometry and the material properties of the metaphysical bone are copied exactly for the computer model.